acute angle - an angle that is less than 90°.
equilateral triangle - a triangle whose sides are all the same length.
isosceles triangle - a triangle that has two sides the same length (and two angles the same).
obtuse angle - an angle that is greater than 90°.

right angle - an angle that measures exactly 90°.
right triangle - a triangle that has one interior angle that is exactly 90°. Note, some right triangles are also scalene triangles.
scalene triangle - a triangle whose sides are all different lengths. Note, some scalene triangles are also right triangles.
straight angle - an angle that measures 180°.